Typically, a device responsible for routing data through a computer network, such as a router, implements one or more intra-network routing protocols commonly referred to as interior gateway protocols (IGPs) to exchange routing information describing links or paths within a network domain. Example IGPs include an Intermediate System to Intermediate System (IS-IS) routing protocol and an Open Shortest Path First (OSPF) routing protocol. The router may then resolve the routing information by selecting a path through the network for reaching each available destination within the network and generating forwarding information, which may be used to forward data packets through the computer network.
Both the IS-IS and OSPF routing protocols fall within a class of routing protocols referred to as link-state protocols. Link state protocols advertise or otherwise facilitate the exchange of routing information by generating and transmitting link state advertisements describing a state of a link between any two adjacent routers within the computer network. These link state advertisements may include information identifying an interface cost or metric associated with an interface to which the link connects and a link cost or metric associated with the link.
Another routing protocol is Border Gateway Protocol (BGP). BGP route reflection is one way to distribute BGP routes between BGP speakers belonging to the same administrative domain. In layer three (L3) Virtual Private Network (VPN) scenarios, a Route Reflector (RR) is not placed in the forwarding path of the packet, but requires the traffic to be tunneled from an Autonomous System (AS) ingress Provider Edge (PE) router to an egress PE router of the network.
‘Hot-potato-routing’ refers to a common routing paradigm in these BGP deployments that attempts to direct traffic to the closest AS egress point in cases where no higher priority policy dictates otherwise. As a consequence of the route reflection method, the choice of egress point for an RR and its clients will be the egress point closest to the RR and not necessarily closest to the RR clients.